Process for forming a-axis-on-c-axis double-layer oxide superconductor films

Abstract

A process for forming a laminate of 123-type copper oxide superconductor thin films having dissimilar crystal axis orientations, a laminate of 123-type thin copper oxide superconductor layers exhibiting excellent superconducting property, and wiring for Josephson junction. A c-axis oriented single crystalline thin film of an oxide superconductor having a Y:Ba:Cu atomic ratio of substantially 1:2:3 and a lattice constant of 11.60 angstroms</=c</=11.70 angstroms at a temperature of 20 DEG C. under an oxygen partial pressure of 160 Torr is formed on a single crystalline substrate, and an a-axis oriented single crystalline thin film of said oxide superconductor is formed on the above laminated film relying upon a sputter deposition method.

We claim: 
     
       1. A process for forming an oxide superconductor thin film comprising: forming a c-axis-oriented single crystalline thin film of an oxide superconductor having a Y:Ba:Cu atomic ratio substantially equal to 1:2:3 and a lattice constant of 11.60 angstroms≦c≦11.70 angstroms at a temperature of 20° C. under an oxygen partial pressure of 160 Torr on a single crystalline substrate,   heat-treating the c-axis-oriented single crystalline thin film of the oxide superconductor at a temperature of from 600° C. to 850° C. under an oxygen partial pressure of from 0.1 mTorr to 100 mTorr, and   forming an a-axis-oriented single crystalline thin film of the oxide superconductor on the heat-treated c-axis-oriented single crystalline thin film by a sputtering method.   
     
     
       2. The process for forming an oxide superconductor thin film according to claim 1, wherein a pulse laser deposition method is employed for forming the c-axis-oriented single crystalline thin film. 
     
     
       3. The process for forming an oxide superconductor thin film according to claim 1, wherein the substrate is obtained by epitaxially growing a buffer layer on a single crystalline substrate. 
     
     
       4. The process for forming an oxide superconductor thin film according to claim 1, wherein an SrTiO 3  (100) single crystal is used as the single crystalline substrate. 
     
     
       5. A process for forming an oxide superconductor thin film comprising: providing an SrTiO 3  (100) single crystal as a substrate,   forming a c-axis oriented single crystalline thin film of an oxide superconductor having the formula YBa 2  Cu 3  O 7-x , wherein x is a number between zero and 1, and a lattice constant of 11.60 angstroms≦c≦11.70 angstroms at a temperature of 20° C. under an oxygen partial pressure of 160 Torr on the substrate by a pulse laser deposition method while maintaining the substrate at a temperature of 600° C. to 850° C.,   heat-treating the thin film at a temperature of 600° C. to 850° C. under an oxygen partial pressure of 0.1 mTorr to 100 Torr, and   laminating an a-axis-oriented single crystalline thin film of the oxide superconductor on the c-axis-oriented thin film by a sputter deposition method while maintaining the substrate at a temperature of from 500° C. to 800° C.